The invention relates to friction clutches and to assemblies which employ engageable and disengageable friction clutches, and more specifically to improvements in apparatus for operating friction clutches, especially in the power trains of motor vehicles. Such clutches are engaged when the prime mover (such as an internal combustion engine and/or an electric machine) drives or is driven by the wheels of the motor vehicle but are disengaged during shifting of the transmission into a gear ratio or into a different gear ratio.
German patent No. 43 13 346 discloses a so-called central clutch engaging and disengaging apparatus (hereinafter called apparatus or clutch actuating apparatus). The apparatus is a hydralically operated arrangement including a so-called slave cylinder and piston unit which is coaxial with the rotary input element of a change-speed transmission. The unit comprises a cylinder which is separably secured to the case (housing) of the transmission, and an annular piston which is reciprocable at one axial end of an annular plenum chamber bounded from without by the aforementioned cylinder and from within by a tubular sleeve-like guide spacedly surrounding the input element (such as a shaft) of the transmission. An end portion of the sleeve-like guide is provided with an annular reinforcement which is adjacent (a) one end portion of the cylinder and (b) the transmission case when the clutch actuating apparatus is installed in the power train of the motor vehicle. The piston bounds one end of the plenum chamber and is provided with an annular seal slidably engaging the internal surface of the cylinder and the external surface of the sleeve-like guide. That end portion of the piston which is remote from the transmission case carries a bearing serving to disengage the clutch (e.g., by engaging the customary radial prongs of and by thus tilting a diaphragm spring of the clutch) when the plenum chamber receives an adequate supply of pressurized hydraulic fluid so that the piston is moved axially and away from the transmission case through a distance which suffices to disengage the clutch. Pressurized fluid is caused to flow into and from the plenum chamber through a passage provided in a radially projecting extension which is carried by the cylinder. The extension is further provided with an aerating passage which also communicates with the plenum chamber and serves to convey flows of a gaseous fluid, such as air.
The cylinder and the sleeve-like guide of the aforedescribed clutch actuating apparatus are two separately produced parts made of sheet metal and having end portions which are adjacent the transmission case and are permanently and sealingly connected to each other. The cylinder has an opening which receives one end portion of the aforedescribed extension, and such one end portion is soldered to the cylinder.
The extension, the cylinder and the sleeve-like guide are made of steel, i.e., the major part of the apparatus consists of steel, mainly of sheet steel stock. The assembly of the cylinder with the separately produced sleeve-like guide and with the separately produced extension takes up much time and such constituents of the apparatus must be produced and shaped in separate machines or production lines. All this contributes considerably to the cost of the slave cylinder and piston unit and of the entire clutch actuating apparatus as well as to the cost of the power train. Furthermore, the weight of the fully assembled unit including the steel cylinder, the steel guide and the steel extension is quite pronounced. Moreover, the assembled combination of cylinder, guide and extension embodies two potential weakened zones which are prone to leakage, namely one between the interconnected end portions of the cylinder and the guide, and the other between the cylinder and the extension.
Published German patent application A 41 29 370 discloses a modified clutch actuating apparatus wherein the slave cylinder and piston unit employs a one-piece plastic cylinder. The cylinder is preferably made of a thermosetting plastic material (preferably in an injection molding machine) because it is provided with at least one undercut portion and must be capable of yielding in the region of such undercut portion. Furthermore, the plastic cylinder must be provided with a thick wall (as measured radially of the slave cylinder and piston unit) in order to ensure that such cylinder will be capable of predictably withstanding the anticipated radial, axial and/or other stresses. This contributes to the bulk of the slave cylinder and piston unit. Still further, the one-piece thermosetting cylinder exhibits the tendency to undergo highly pronounced thermally induced expansion which affects the quality of the sealing action between such cylinder and the piston of the slave unit; this can be counteracted by resorting to a complex and hence bulky and highly expensive sealing arrangement between the cylinder and the piston.
An object of the instant invention is to provide a cylinder and piston unit which embodies the advantages but does not exhibit the drawbacks of the aforedescribed cons ventional cylinder and piston units.
Another object of the invention is to provide a cylinder and piston unit which can be utilized with advantage as a central slave cylinder and piston unit in the system for actuating the friction clutch of the power train in a motor vehicle.
A further object of the invention is to provide a compact, relatively inexpensive, deformation-resistant and hence long-lasting cylinder and piston unit for use in a clutch engaging/disengaging apparatus.
An additional object of the invention is to provide a novel and improved method of assembling a cylinder and piston unit for use as a means for actuating a friction clutch in the power train of a motor vehicle.
Still another object of the invention is to provide a power train which embodies at least one cylinder and piston arrangement or unit of the above outlined character.
A further object of the invention is to provide a novel and improved separable coupling between the constituents of a composite cylinder which is or which can be utilized in the above outlined cylinder and piston unit.
Another object of the invention is to provide a novel and improved separable connection between the cylinder of the above outlined cylinder and piston unit and a support therefor, e.g., the housing or case of a change-speed transmission in the power train of a motor vehicle.
An additional object of the invention is to provide a novel and improved connection between the cylinder of the above outlined slave cylinder and piston unit and a master cylinder which controls the operation of the slave cylinder and forms part of the clutch engaging/disengaging apparatus in the power train of a motor vehicle.
The invention is embodied in a novel and improved combination of parts which can be utilized in a clutch engaging and disengaging apparatus and comprises a hydraulic cylinder and piston unit including a composite cylinder having a tubular synthetic plastic outer wall, a tubular metalic inner wall spacedly surrounded by the outer wall, and means for coupling the inner and outer walls to each other. The combination further comprises a support (such as the housing or case of a change-speed transmission in the power train of a motor vehicle) for at least one of the walls.
The means for coupling the inner and outer walls to each other can comprise a snap fastener. The outer wall preferably comprises a substantially annular first end portion, and the inner wall can comprise a substantially annular second end portion adjacent the first end portion; the snap fastener of such composite cylinder can include means for securing the first and second end portions to each other.
The outer wall is preferably provided with an unfinished internal surface (i.e., the finish of such surface can match the finish when the making of the outer wall, e.g., in an injection molding machine, is completed). The internal surface is spaced apart from the external surface of the inner wall, and the novel combination further comprises an annular piston which is reciprocable along the internal surface of the outer wall and is movable around the inner wall. The piston preferably includes a suitable seal which engages the internal surface of the outer wall.
The outer wall is or can constitute a molding, preferably a molding which is a product of an injection molding technique.
The internal surface of the outer wall can constitute a conical surface having a conicity of at least 0.5xc2x0; the advantage of such conical internal surface will be pointed out hereinafter. The orientation of the cylinder is preferably such that the reciprocable piston between the inner and outer walls has a first end remote from and a second end nearer to the support. The first end of the piston serves to reciprocate a clutch release bearing which can engage or release the customary radially inwardly extending fingers or prongs of the clutch spring, such as a diaphragm spring. The conical internal surface of the outer wall tapers (i.e., its diameter diminishes) in a direction toward the support.
The plastic material of the outer wall is preferably a thermosetting plastic, e.g., a material selected from the group consisting of phenolic plastics, amino plastics, epoxy resins and unsaturated polyester resins.
The at least one wall which is connected to the support is or can constitute the outer wall of the cylinder, and the means for securing the outer wall to the support can include external eyelets or grommets provided on that end portion of the outer wall which is adjacent the support and fasteners extending through the eyelets and engaging (particularly penetrating into) the support. Such securing means can further comprise prestressed resilient reinforcing sleeves which are disposed in the eyelets, which surround portions of the respective fasteners and which tend to expand radially outwardly against the internal surfaces of the respective eyelets. If the fasteners are threaded fasteners (such as bolts or screws each having a threaded shank and a head at one end of the shank), one end of each of the resilient sleeves can be provided with a collar located between one side of the respective eyelet and the head of the respective threaded fastener.
The aforementioned means for coupling the inner and outer walls to each other can be designed in such a way that its parts are constituted by one end portion of the outer wall and the adjacent end portion of the inner wall, particularly by those end portions of the two walls which are adjacent the support. The end portion of the inner wall can include at least one annular reinforcing section (e.g., a reinforcing section having a substantially U-shaped cross-sectional outline and being receivable in a complementary recess of the support). The means for coupling can include an undercut substantially annular socket provided in one of the two end portions (e.g., in the end portion of the outer wall), and a substantially annular male connector which is removably received in the socket by snap action and forms part of the other end portion. The end portion which defines the socket can be provided with a substantially annular ramp bounding a portion of the socket and being arranged to guide the male connector into the socket during actual coupling of the two walls to each other.
One end portion of the outer wall can be provided (and is preferably of one piece) with an extension, particularly a radially outwardly projecting extension. The extension has at least one fluid conveying passage which communicates (or can be caused to communicate) with the aforementioned annular plenum chamber between the inner and outer walls. That end of the at least one passage which is remote from the one end portion of the outer wall can be sealed by a plug or other suitable sealing means.
The outer wall can carry a suitable valve which can be utilized to ventilate (when necessary) the plenum chamber. The valve can be carried by the aforementioned extension of the outer wall; such extension can be provided with several passages one of which is controlled by the valve and another of which serves to introduce pressurized hydraulic fluid into and/or to permit evacuation of hydraulic fluid from the chamber.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved combination itself, however, both as to its construction and the modes of assembling the same and of incorporating it in a clutch actuating apparatus, together with numerous important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.